I. Technical Field
The present invention relates to a driving-wheel bearing device which rotatably supports a driving wheel (front wheel of a front-engine front-drive (FF) vehicle, rear wheel of a front-engine rear-drive (FR) vehicle, and all wheels of a four-wheel drive (4WD) vehicle) with respect to a suspension device for, for example, an automobile.
II. Description of the Related Art
Bearing devices for automobiles include ones for driving wheels and ones for driven wheels, and there have been proposed ones of various types in accordance with respective applications. For example, FIG. 16 illustrates a driving-wheel bearing device. The bearing device includes the following as main components: a hub wheel 210 and an inner race 220, double-row rolling elements 230 and 240, an outer race 250, and a constant velocity universal joint 260.
The hub wheel 210 has an outboard-side inner raceway surface 212 formed on an outer peripheral surface thereof, and includes a wheel attachment flange 214 for allowing a wheel (not shown) to be attached thereto. Hub bolts 216 for fixing a wheel disk are equiangularly embedded in the wheel attachment flange 214. The inner race 220 is fitted to a small-diameter step portion 218 formed on the outer peripheral surface of the hub wheel 210, and an inboard-side inner raceway surface 222 is formed on an outer peripheral surface of the inner race 220. A female spline 211 for coupling the constant velocity universal joint 260 with the hub wheel 210 so that torque can be transmitted therebetween is formed on an inner peripheral surface of a shaft hole of the hub wheel 210.
The inner race 220 is press-fitted to the small-diameter step portion 218 of the hub wheel 210 with adequate tightening margin for the purpose of preventing creep. The outboard-side inner raceway surface 212 formed on the outer peripheral surface of the hub wheel 210 and the inboard-side inner raceway surface 222 formed on the outer peripheral surface of the inner race 220 constitute double-row inner raceway surfaces. The inner race 220 is press-fitted to the small-diameter step portion 218 of the hub wheel 210, and the end portion of the small-diameter step portion 218 of the hub wheel 210 is crimped outward. As a result, the inner race 220 is prevented from slipping off by a crimped portion 213 thus formed, and is integrated with the hub wheel 210, to thereby apply preload to a bearing section 270.
The outer race 250 has double-row outer raceway surfaces 252 and 254 formed on an inner peripheral surface thereof and opposed to the inner raceway surfaces 212 and 222 of the hub wheel 210 and the inner race 220, and includes a vehicle body attachment flange 256 for being attached to a vehicle body (not shown). The vehicle body attachment flange 256 is fixed, with use of an attachment hole 258, by bolts or the like to a knuckle extending from a suspension device (not shown) of a vehicle body.
The bearing section 270 has a double-row angular ball bearing structure, specifically, has the following structure: the rolling elements 230 and 240 are interposed between the inner raceway surfaces 212 and 222 formed on the outer peripheral surfaces of the hub wheel 210 and inner race 220 and the outer raceway surfaces 252 and 254 formed on the inner peripheral surface of the outer race 250; the rolling elements 230 and 240 in respective rows are rotatably and equiangularly retained by retainers 232 and 242.
At the openings on both ends of the bearing section 270, a pair of seals 234 and 244 for sealing annular spaces between the outer race 250 and the hub wheel 210 and between the outer race 250 and the inner race 220 so as to be held in sliding-contact with the outer peripheral surfaces of the hub wheel 210 and inner race 220 are fitted to the inner periphery at both end portions of the outer race 250. Further, the seals 234 and 244 prevent leakage of lubricant filling the inside and intrusion of water and foreign matters from the outside.
An outer joint member 262 of the constant velocity universal joint 260 is coupled with the hub wheel 210, and hence a bearing device is constituted. The outer joint member 262 of the constant velocity universal joint 260 is provided at one end of an intermediate shaft (not shown) constituting a drive shaft, and is constituted by the following: a cup-shaped mouth section 264 housing inner components (not shown) including an inner joint member, balls, and a cage; and a stem section 266 extending integrally from a proximal portion of the mouth section 264 in an axial direction. A male spline 268 for coupling the hub wheel 210 with the constant velocity universal joint 260 so that torque can be transmitted therebetween is formed on an outer peripheral surface of the stem section 266.
The stem section 266 of the outer joint member 262 is press-fitted to the shaft hole of the hub wheel 210, and the male spline 268 formed on the outer peripheral surface of the stem section 266 and the female spline 211 formed on the inner peripheral surface of the shaft hole of the hub wheel 210 are fitted to each other. In this manner, torque can be transmitted. Further, in a state in which opposite surfaces of the crimped portion 213 of the hub wheel 210 and a shoulder portion 261 of the outer joint member 262 are hit against each other, a nut 272 is tightened to a male-screw portion 265 formed at an end portion of the stem section 266. In this manner, the constant velocity universal joint 260 is fixed to the hub wheel 210.
Incidentally, in the driving-wheel bearing device, the crimped portion 213 of the hub wheel 210 of the bearing section 270 and the shoulder portion 261 of the outer joint member 262 are in a contact state of being hit against each other. Thus, upon starting of a vehicle, there is a risk that stick-slip noise commonly known as squeaking noise is generated between the crimped portion 213 of the hub wheel 210 of the bearing section 270 and the shoulder portion 261 of the outer joint member 262.
The stick-slip noise means noise generated by abrupt sliding caused as follows: upon starting of a vehicle, although rotational torque is applied from the outer joint member 262 of the constant velocity universal joint 260 with respect to the hub wheel 210 of the bearing section 270 in a static state so as to be transmitted from the outer joint member 262 to the hub wheel 210 through intermediation of the female spline 211 and the male spline 268, the transmitted torque between the bearing section 270 and the outer joint member 262 varies and the outer joint member 262 twists, with the result that abrupt sliding occurs between the crimped portion 213 of the hub wheel 210 and the shoulder portion 261 of the outer joint member 262.
As means for preventing the stick-slip noise, there has been provided means for sandwiching a plate excellent in sliding properties between the opposite surfaces of an inboard-side end portion of the bearing section 270 and the shoulder portion 261 of the outer joint member 262 (refer to JP 2003-97588 A and JP 2007-508986 A).
In JP 2003-97588 A and JP 2007-508986 A mentioned above, the plate is interposed between the opposite surfaces of the inboard-side end portion of the bearing section 270 and the shoulder portion 261 of the outer joint member 262. As a result, frictional resistance is reduced between the opposite surfaces of the inboard-side end portion of the bearing section 270 and the shoulder portion 261 of the outer joint member 262 so that positive sliding is caused. Thus, abrupt sliding is not caused, and hence generation of stick-slip noise is prevented.